Sydney researchers have found that indoor plants improve the air quality of rooms with little or no airflow.

A team led by Adjunct Professor Margaret Burchett at the University of Technology, Sydney, have found that common indoor potted plants such as the Peace Lily and the Kentia Palm improve indoor air by reducing levels of volatile organic compounds, or VOCs.

The scientists found that indoor plants reduce VOCs by up to 100 per cent over 24 hours in a closed environment.

VOCs include compounds such as benzene and hexane, and are known to be toxic to humans at high levels. They are present at low levels in many indoor environments. Some, like benzene, make their way inside buildings through pollution from traffic outside. Others are present as a result of their use in paints, carpeting, and furniture fabric, especially in new or recently refurbished buildings.

According to Dr Stephen Brown of CSIRO Built Environment, VOCs can contribute to 'sick building syndrome'  a phenomenon in which a higher proportion of occupants experience symptoms such as dry eyes, dry nose and throat, headache, lethargy, and nausea.

"Indoor air is likely to be five and seven times more polluted than outdoor air  unless you are right on the freeway  because indoor air is stale and it accumulates. And this is with or without air-conditioning," said Professor Burchett.

The researchers trialed seven different species of common indoor potted plants in 200-litre sealed chambers. They found that the pollutants were removed from the air predominantly by the metabolic activities of soil microorganisms associated with the plant roots.

"Because plants have a lot of surface area on the leaves, we thought that they were probably taking it up through the tiny pores on the leaves," said Professor Burchett.

However, even when the plants were covered with black plastic to reduce their metabolic level, the pollutants were still removed from the air.

"It was a clear indication that it was the microorganisms in the potting mix that were doing it."

These soil microorganisms exist in a symbiotic relationship with the plant, providing the plant with inorganic nutrients from the soil and in return receiving other nutrients from the plant via the roots.

The group is currently looking into performing research in real-life situations, such as an office environment with a small amount of flow-through air.

"We have people falling over themselves to volunteer their horrible offices for us to work in," said Professor Burchett.

Preliminary findings have shown that indoor plants and their associated microorganisms were successful in removing between 10 and 20 percent of pollutants in areas with flow-through air.

The group will also be looking into the number of plants needed in order for this effect to become apparent.

"It is not true that you have to have a rainforest," said Professor Burchett. "But as many as you can get commensurate with reasonable design is obviously better."

She said that plant breeding and horticultural improvements to enhance the capacity of these types of plants is also on the agenda.

"If we can do horticultural development to get black tulips and blue carnations, we can develop something so that the pot plant microcosm can take out more gunk from the air."